* How the Universe was Created. Here is a summary of Hesiod's Theogony:

In the beginning, there was the void, Chaos. And from that void emerged Gaia. She had some children in parthenogenetic fashion, including her partner Ouranos. This couple had several more children, including Kronos and his fellow Titans. But Kronos rebelled against Ouranos, castrating him. And Kronos and his partner Rhea had kids of their own. But Kronos was afraid that they would do to him what he had done to Ouranos, so he swallowed them as they were born. Rhea got tired of having kids for nothing, so when she had Zeus, she had him sent away and she fed a bundled stone to Kronos. Zeus eventually grew up and forced Kronos to vomit up his brothers and sisters. And Zeus and his Olympian friends overthrew Kronos, becoming the new rulers of the Universe.

That is an anticipation of the Big Bang, since according to some quantum-cosmological speculations, the Universe originated from a quantum fluctuation in a void. And as it expanded, it went through several generations of structure. The earlier generations are still murky, but the later ones are well-understood: a quark-soup phase, then a hadron-soup phase, then a lepton-soup phase, and then a photon-soup phase, which we are still in. In that phase, there were first electrons, protons, and neutrons, then electrons and light nuclei, and then light atoms -- mostly hydrogen and helium.

When stars formed, they went through some generations. The first one, "Population III", was mostly massive, short-lived stars, but it produced enough heavier elements ("metals") to allow lower-mass stars to form. These were the "Population II" stars, which we can still see in the Galactic center, the Galactic halo, and the globular clusters. This was succeeded by a more recent generation, "Population I", in the Galactic disk; the Sun belongs to that generation.

Likewise, life on Earth has had numerous generations. This is a very complicated subject; I'll give an overall view and then some subviews. The first generation of life on Earth was various chemosynthesizers (they live off of chemical reactions) and anaerobic photosynthesizers (they do not release oxygen). At about 2.3 billion years ago, this was followed by a generation of cyanobacteria (blue-green "algae") and oxygen-utilizing bacteria. This was followed at about 1.5 billion years ago by the first protists, some of which became inhabited by their favorite food -- various bacteria. And about 600 million years ago was the beginning of the multicelled-animal generation. However, these generations have largely been cumulative; earlier ones coexist with later ones.

The earliest generation likely has subgenerations of prebiotic chemistry, the RNA world, the first RNA-protein systems, the first RNA-genome cells, and the first DNA-genome cells. And of later generations, I'll confine myself to land plants. The first of these, starting perhaps a billion years ago or more, were soil algae. These were followed about 450 million years ago by the generation of the mosses and liverworts and other such primitive land plants. Which, in turn, were followed by a generation of early vascular plants, like ferns, horsetails, and club mosses. Which were followed about 350 million years ago by early seed plants (gymnosperms). Which were followed about 150 million years ago by the generation of flowering plants (angiosperms). These have been somewhat cumulative; there are stragglers from the earlier generations still alive today.

* Divine Intervention in History. The Iliad, the Odyssey, and other such documents are full of Olympian intervention in history, such as the Olympians taking sides in the Trojan War.

By the nineteenth century, the historicity of these stories was seriously questioned, but Heinrich Schliemann caused a sensation when he discovered a city at where the Iliad had described Troy as being located. Which means that the Iliad contains some real history. And could it also mean that the Iliad is also correct about asserting the existence of the Olympians?

Later archeological work would discover several other "mythological" places, like Mycenae, Tiryns, Pylos, and Knossos, and would confirm the presence of such items described in the epics as bronze armor and boar's-tusk helmets, and the worship of the familiar Olympians there. There was even confirmation of a "literacy gap" in the Greek world between the Mycenaeans and Classical times; the only reference to writing in the Iliad is a tablet with "magic signs". And at Knossos, a very labyrinthine palace was discovered, where a "Mistress of the Labyrinth" was worshipped, and where there were odd bull-riding ceremonies (not quite a Minotaur, but...).

Also, the Odyssey describes a certain people, the Laestrygonians, as living at a long harbor surrounded by rocky cliffs, and experiencing continual daylight. Which has a close resemblance to a Scandinavian fjord, complete with continual daylight during the summer, the most likely time to visit by sea.

* Oracles. These were widely consulted, and even fought over in the "Sacred Wars"; the most famous ones were Apollo's at Delphi and Zeus's at Dodona. They stayed in business for hundreds of years; why had they been in business for so long if the Olympians were pure fiction? Even the eminent historian Herodotus acknowledged their validity.

* Divine Parentage. Zeus, especially, had numerous offspring; it was not for nothing that he was called "Father Zeus". In fact, Pythagoras and Plato had supposedly had Apollo as their biological father, and Alexander the Great had supposedly had Zeus as his biological father. And there is an abundance of evidence for the existence of these gentlemen, meaning that we ought to give at least a little credence to the divine-parentage theory. Their being unusual achievers also points to superhuman parents; would normal men be capable of siring such great men?

* Dreams and Visions. Lucretius, a follower of Epicurus and a skeptic about deities in general, attempted in his work "On the Nature of Things" to account for the dreams and visions that people would have of these deities -- which is an implicit acknowledgment of their reality.

* Early Christian Apologists. Though being violently opposed to the worship of the Olympians, calling that worship an invention of the Christian Devil, they never bothered to deny the existence of those deities, almost as if they were aware of the reality of these deities.

* Cures. There were several temples of Asklepios, son of Apollo. One would go to such a temple and spend the night there there, and Asklepios would communicate a prescription in a dream. And Asklepios's temples have lots of testimonials on their walls. Were they all fakes or fantasies?

And the Hippocratic Oath features swearing by Apollo and Asklepios and some other Olympians; the endurance of this oath suggests that these deities were worth worshipping. Furthermore, modern medicine follows in the mechanistic, rationalistic tradition of Hippocrates, which is yet more evidence for the existence of these deities.

* Science in general. Such eminent early scientists as Aristotle, Archimedes, Hipparchus, Ptolemy, etc. had been raised on the worship of the Olympians; science went into eclipse as their worship went into eclipse. However, the Renaissance saw not only revived interest in the Olympians, but also the restarting of science. Could this be a coincidence?

* Greece Surviving the Persians. Persia never succeeded in conquering Greece in the Persian Wars of ~500 BCE despite the Persians having much bigger armed forces. Could it be that the Greek people were protected by some deities? And could those deities be the ones that they had worshipped? Herodotus tells us that Athena herself took part in the battle, in the form of an owl.

Furthermore, Greek ethnicity went into partial eclipse when the Greeks stopped worshipping their old deities. The Byzantines preferred to think of themselves as "Romaioi" rather than Greeks -- and they were eventually conquered by the Ottoman Empire.